1. Field of the Invention
The present invention relates to a production/injection line, comprising a production/injection tube and heating means for active heating of the tube, a method for supplying heat to a production/injection line and a method for manufacturing a production/injection line, comprising a production/injection tube which comprises a plurality of elongate members, including a core tube, which shall serve as an injection/production tube, pipes and/or cables arranged outside the core member and channel members containing channels in which the pipes and/or cables are freely movable, and a protective outer casing.
2. Description of the Related Art
Such pipelines are used for the transport of oil and/or gas between subsea installations and between subsea installations and a platform or vessel on the surface of the sea. Pipelines of this type can also be used for injection in a well.
Parallel with such production/injection lines, there are as a rule also laid one or more control cables, which are generally gathered into a control cable bundle, or a so-called “umbilical.”
An umbilical of this type is known from, for example, NO 174,940 of the same applicant, where a core member, for transport of chemicals for injection in a well, is surrounded by control cables for the transfer of hydraulic fluid, electrical and optical signals, electrical power, etc.
It is known to bundle together the production line and the control cables so that these run next to each other over the whole, or parts of the distance. By this means the risk of rupture and other damage to the cables is reduced, at the same time as it becomes easier to lay them out and, if necessary, to retrieve them again. However, the cables will have to be connected separately to the equipment on the seabed or on the surface, and it is thus necessary to have both a connector for the production line and a connector for the control cables. This connecting process takes considerable time and involves significant costs, in addition to occupying a relatively large area.
From GB 1,210,206 it is known to integrate the control cables with the production line by having the control cables wound around the production line. This ensures that the production line and the control cables will always stay together.
Also, it is desirable to hold the temperature of the production fluid (oil and/or gas) in the production line as high as is practically possible, which is to say a temperature of 50-100° C. This is because a lower temperature could cause the production fluid to have a higher viscosity and, as a result, to have a reduced flow rate. In addition, it is possible for wax to form, which accumulates on the tube wall and narrows the cross section of the tube.
There have been attempts to avoid this problem by means of the pipeline according to EP 521,582, where electrical heating cables are arranged next to the pipeline. There is also arranged an insulation layer around the pipeline. In NO 170,695 the heat loss from electrical transmission elements is used to heat up the pipeline.
The disadvantage with this known art is primarily that the electrical cables require special equipment for the generation of electrical current. The heating cables require considerable energy and can also represent an explosion risk.